Fair value as of the balance sheet date of all interest rate derivative liabilities designated as cash flow hedging instruments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 17

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_InterestRateCashFlowHedgeLiabilityAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Accounting Policies (Details) (USD $)	3 Months Ended
Accounting Policies (Details) (USD $)	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Recurring Fair value Cash flows approach	Dec. 31, 2012 Recurring Fair value Cash flows approach	Mar. 31, 2013 Recurring Significant Other Observable Inputs (Level 2) Cash flows approach	Dec. 31, 2012 Recurring Significant Other Observable Inputs (Level 2) Cash flows approach
Revenue Recognition
External freight billed to customer included in revenue	$ 6,000,000	$ 6,800,000
Fair Values of Financial Instruments
Interest rate swap liabilities			$ (2,335,000)	$ (2,629,000)	$ (2,335,000)	$ (2,629,000)